Look up basil downy mildew and compare. If it is, I am sorry because I don't think the copper will help for long. Nasty!

No it is not downy mildew. I had that last summer. I know what that looks like and how the plant would act prior to the mildew showing up. And it is not spreading.

Also - the basil is Eleanora which is suppose to have some resistance to it.

It doesn't look like a fungus to me, just from the leaf. If I were to guess what the problem was, I'd say either oxygen deprivation from water-logged roots or a nutrient deficiency of some kind, most likely potassium from the information you've given.

Any other symptoms besides the markings and the chlorosis? Are the stems looking normal? Any sign of wilting, leaf drop or leaf curl? Any sign of insects anywhere? If you can spare one of the sick-looking plants, dig it up and have a look at the roots.

Thanks Sophie! I will do that. I know there is a nutrient deficiency, I did do a nitrogen foliar spray on everything since we have had so much rain and I cannot water nutrients in. I will get some kelp to work into the top of the soil. I was doing some research and thought maybe it was black spot or leaf spot. It looks like soot to me but it does not match pictures on the net of black soot mold. I have a lot of it covered with tarps right now because we are again getting record rains. {Sigh}

Sorry - no signs of wilting, leaf drop (except the bottom ones with this spotting) or leaf curl. Some minor bug damage but chewing damage not like aphids or thrips.

Sophie is on the right path, I believe. As plants cut off the energy supply to their leaves, for whatever reason, they will yellow and are often attacked by disorders that a healthy leaf will fend off easily.

I don't know that there's a thing you can do considering all of the rain you've been having. The problem is at the root zone....the yellow, spotted leaves are merely the symptom.

Okay. I wouldn't worry about it too much then. Once the excess moisture drains away, you can get some extra nutrients into the soil and I should think that it will stop.
Of the handful of fungal and bacterial leaf spots that basil growers normally have to worry about, that doesn't resemble any of them. To me the spots are most likely either a symptom of the malnutrition or something minor that the plant's immune system normally destroys wherever it's got its full strength, like Rhizo said.
The tarps are a good idea. I had to do that a couple of months ago when we had some unprecedented flooding and hail. My holy basil plants died, but the other basils pulled through okay. I think 300 of them would test my resolve, though. :)

They are testing my resolve! So is this rain! About to build myself an ark and load it with basil instead of animals! I did use Al's mix from the container forum which is a very fast draining soil. But it is lacking in nutrients. The idea being that I would control adding them. I have transplanted some and added a slow release fertilizer into each bucket to help. Live and learn! I will post a picture of an actual plant in a little bit so you can see the full effect of what I am talking about. Once it stops raining! Thanks! You guys are a big help! I hope it is just a nutrient problem. Last year's downy mildew debacle really has me on edge this year!

Hey all - as promised here are some pics of plants. Thanks again for your help. We did have a break in the rain yesterday so I was able to give all the basil a good feeding. Still tarping them (which is not ideal but I don't want to lose it all to root rot.)